Luminescence titrations

The values of the binding constants determined with different salt concentrations by equilibrium dialyses [43, 48], luminescence titrations and electrochemiluminescence [82], are all 2 or 3 orders of magnitude lower than for ethidium bromide. Therefore, a priori, they do not indicate contribution of classical intercalation into DNA as described for organic molecules and for the DPPZ, HAT and PPZ complexes. 

Fig. 10 Luminescence titration curves for the titrations of (1) 3.8 xM avidin ( ), (2) 3.8 jiM avidin and 380.0 jiM unmodified biotin ( ), and (3) a blank phosphate buffer solution ( ) with [Re(Me2-Ph2-phen)(CO)3(py-4-CH2 -NH-C6-NH-biotin)]+ [68]...

Luminescence titrations further demonstrate that the ruthenated duplex behaves as a 15 mer bearing one intercalator (76). As free [Ru(phen)2(dppz)]2+ is added to a solution of unmetallated 15 mer duplex, the luminescence increases linearly until the emission reaches saturation at about three equivalents of ruthenium(II) per duplex, consistent with competitive binding of [Ru(phen)2(dppz)]2+ to the 15-mer duplex and an average binding site size of a little more than four base pairs. When the analogous experiment is conducted with the ruthenated duplex, saturation of luminescence occurs after almost two equivalents of [Ru(phen)2(dppz)]2+ are added. This comparison indicates that the covalently bound ruthenium(II) complex is not displaced by additional intercalators. 

Figure 13.13 Chemical structure of Tb-29 and luminescent titrations of Tb-29 (10 jlM) in CH3CN upon addition of F , CC, Br, I, CIO, NOj, NO2, and AcO [50]. (Reproduced with permission from D.Q. Zhang et al., The luminescence modulation of a terbium complex with fluoride anion and its application for chemodosimeter , European Journal of Inorganic Chemistry, 2006, no. 11, 2277-2284. Wiley-VCH Verlag Gmbh Co. KGaA.)...

Titrimetric luminescence methods record changes in the indicator emission of radiation during titration. This change is noted visually or by instruments normally used in luminescence analysis. Most luminescence indicators are complex organic compounds which are classified into fluorescent and chemiluminescent, compounds according to the type of emission of radiation. As in titrimetry with adsorption of colored indicators, luminescence titration makes use of acid-base, precipitation, redox, and complexation reactions. Unlike color reactions, luminescence indicators enable the determination of ions in turbid or colored media and permit the detection limit to be lowered by a factor of nearly one thousand. In comparison with direct luminescence determination, the luminescence titrimetric method is more precise. 

Luminescence titration has extensively been described in several mono-graphs4-6, u 708 Fluorimetric and chemiluminescence indicators are used for the determination of about 30 elements (Fig. 3). 

Metal ion complexes can form an imprint site that exhibits both a spectral signature and can be expected to survive incorporation into a pol)oner. A solution analogue of the imprint site can be prepared and the utility for use in imprinting may be established. For a d-block complex, adduction may be characterized by obtaining absorbance, or in some cases, luminescence spectra. The spectral changes that accompany adduct formation are either changes in band position or intensity. Lanthanide-based transduction complexes are usually based on luminescence intensity. If, as in the case of a lanthanide-based reporter, luminescence varies with the degree of analyte inclusion, a luminescence titration will reveal stoichiometry. 

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